RECOVERY OF NANO-STRUCTURED CALCIUM SILICATE HYDRATE FROM GEOTHERMAL BRINE USING A LAMELLA SEPARATOR

Abstract

The formation of silica scale from supersaturated geothermal brine is one of the major challenges of geothermal energy utilization for heat recovery and electricity generation. The scale blocks pipes, valves, heat exchangers and other equipment and reinjection wells. Most current remediation approaches only delay the formation of scale and are not wholly successful. Also, they can lead to advanced corrosion issues.
The competitive transformation of dissolved silica into nanostructured calcium silicate hydrate (NCaSilH) particulate material in the silica supersaturated brine stream prevents the formation of silica scale. The NCaSilH silicate forms rapidly, reducing the amount of available dissolved silica down to safe levels where the dissolved silica species cannot polymerize and precipitate as the problematic silica scale. The NCaSilH particles do not stick to metal, are slightly passivating and can trap other scale forming species like calcium carbonates. However, the silicate hydrate particles are comparatively large and would likely block porous rock media like geothermal reservoirs. This means that NCaSilH needs to be removed from the spent brine prior to reinjection of the brine.
In laboratory tests, the solid liquid separation of NCaSilH particles was investigated in sedimentation and other experiments, which have led to the choice of lamella separation as a promising technology for the recovery of the silicate. Laboratory models were constructed, tested and upscaled. A pilot-scale separator was build, which will be used in two pilot scale test rigs. Present here is the design of the lamella separator and preliminary results from its use.